Even though the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted efforts to increase the fuel economy of automotive engines, the gains continually realized thereby have been deemed by various levels of governments as being insufficient. Further, such levels of government have also imposed regulations specifying the maximum permissible amounts of various pollutants including carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NO.sub.x) which may be emitted by the engine exhaust gases into the atmosphere.
Unfortunately, the available technology employable in attempting to attain increases in engine fuel economy is generally contrary to that technology employable in attempting to meet the governmentally imposed standards on exhaust gas emissions.
For example, the prior art, in trying to meet the standards for NO.sub.x emissions, has employed a system of exhaust gas recirculation whereby at least a portion of the exhaust gas is re-introduced into the cylinder combustion chamber to thereby lower the combustion temperature therein and consequently reduce the formation of NO.sub.x.
The prior art has also proposed the use of engine crankcase recirculation means whereby the vapors which might otherwise become vented to the atmosphere are introduced into the engine combustion chambers for burning.
The prior art has also proposed the use of fuel metering means which are effective for metering a relatively overly rich (in terms of fuel) fuel-air mixture to the engine combustion chamber means as to thereby reduce the creation of NO.sub.x within the combustion chamber. The use of such overly rich fuel-air mixtures results in a substantial increase in CO and HC in the engine exhaust which, in turn, requires the supplying of additional oxygen, as by an associated air pump, to such engine exhaust in order to complete the oxidation of the CO and HC prior to its delivery into the atmosphere.
The prior art has also heretofore proposed retarding of the engine ignition timing as a further means for reducing the creation of NO.sub.x. Also, lower engine compression ratios have been employed in order to lower the resulting combustion chamber and thereby reduce the creation of NO.sub.x.
The prior art has also proposed the use of fuel metering injection means for eliminating the usually employed carbureting apparatus and, under superatmospheric pressure, injecting the fuel into either the engine intake manifold or directly into the combustion chamber means such as the cylinders of a piston type internal combustion engine. Such fuel injection systems, besides being costly, have not proven to be generally successful in that the system is required to provide metered fuel flow over a very wide range. Generally, those injection systems which are very accurate at one end of the required range of metered fuel flows are inaccurate at the opposite end of that same range of metered fuel flows. Also, those injection systems which are made to be accurate in the mid-portion of the required range of metered fuel flows are usually relatively inaccurate at both ends of that same range. The use of feedback means for altering the metering characteristics of a particular fuel injection system have not solved the problem because the problem usually is intertwined within such factors as: effective aperture area of the injection nozzle; comparative movement required by the associated nozzle pintle or valving member; and nozzle "cracking" pressure (that being the pressure at which the nozzle opens). As should be apparent, the smaller the rate of metered fuel flow desired, the greater becomes the influence of such factors thereon.
It is now anticipated that the said various levels of government will be establishing even more stringent exhaust emission limits of, for example, 1.0 gram/mile of NO.sub.x (or even less).
The prior art, in view of such anticipated requirements with respect to NO.sub.x, has suggested the employment of a "three-way" catalyst, in a single bed, within the stream of exhaust gases as a means of attaining such anticipated exhaust emission limits. Generaly, a "three-way" catalyst is a single catalyst, or catalyst mixture, which catalyzes the oxidation of hydrocarbons and carbon monoxide and also the reduction of oxides of nitrogen. It has been discovered that a difficulty with such a "three-way" catalyst system is that if the fuel metering is too rich (in terms of fuel), the NO.sub.x will be reduced effectively but the oxidation of CO will be incomplete; if the fuel metering is too lean, the CO will be effectively oxidized but the reduction of NOX will be incomplete. Obviously, in order to make such a "three-way" catalyst operative, it is necessary to have very accurate control over the fuel metering function of associated fuel metering supply means feeding the engine. Some systems may additionally have a small oxidizing catalyst bed downstream of the three-way catalyst bed to provide further oxidation of CO and HC. Such systems will require that additional oxygen supplied by air pump means be injected downstream of the three-way catalyst bed but upstream of the oxidizing catalyst bed. Such a system can provide very low levels of pollutants in the exhaust gases and also provide a source of air at superatmospheric pressure.
As hereinbefore described, the prior art has suggested the use of fuel injection means with associated feedback means (responsive to selected indicia of engine operating conditions and parameters) intended to continuously alter or modify the metering characteristics of the fuel injection means. However, as also hereinbefore indicated, such fuel injection systems are very costly and have not generally proven to be successful.
It has also heretofore been proposed to employ fuel metering means, of a carbureting type, with feedback means responsive to the presence of selected constituents comprising the engine exhaust gases. Such feedback means were employed to modify the action of a main metering rod of a main fuel metering system of a carburetor. However, tests and experience have indicated that such a prior art carburetor and such a related feedback means can never provide the degree of accuracy required in the metering of fuel to an associated engine as to assure meeting, for example, the said anticipated exhaust emission standards.
Accordingly, the invention as disclosed, described and claimed is directed generally to the solution of the above and related problems and more specificaly to structure, apparatus and systems enabling a carbureting type fuel metering device to meter fuel with an accuracy at least sufficient to meet the said anticipated standards regarding engine exhaust gas emissions.